In photolithography for manufacturing a semiconductor element or the like, an exposure apparatus which projects and exposes a pattern image on a mask (e.g., a reticle) to a photosensitive substrate through a projecting optical system is used. Semiconductor integrated circuits developed recently are aiming at micropatterning. In photolithography, photolithography light sources are going to have shorter wavelengths.
However, when vacuum UV light and, more particularly, light having a wavelength shorter than 250 nm, e.g., harmonic light of a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), F2 laser (wavelength: 157 nm), or a YAG laser is used as exposure light, the intensity of exposure light decreases due to the influence of exposure light absorption by oxygen, and the like.
To avoid the decrease in exposure light transmittance, a conventional exposure apparatus having a light source such as an F2 excimer laser forms a sealed space where only an optical path portion is sealed and replaces the gas in the sealed space with a gas such as nitrogen containing no oxygen.
FIGS. 14A and 14B are views showing an exposure apparatus which performs exposure by supplying an inert gas to a space between a photosensitive substrate (wafer) and the final optical member of a projecting optical system (lens barrel) to form an inert gas atmosphere in the space. In this exposure apparatus, to separate the space on the exposure region from the ambient atmosphere, a shielding member is arranged around the space, and the inert gas is supplied from the periphery of the exposure region into the space.
In the exposure apparatus shown in FIGS. 14A and 14B, however, the atmosphere in the space cannot be replaced with the inert gas until the atmosphere at the step or gap around the wafer moves into the space. In exposing the periphery of the wafer, the inert gas concentration in the space decreases. In addition, when the wafer stage moves at a high speed, the inert gas concentration decreases due to the influence of involvement, resulting in a variation in illuminance.
A similar problem is posed when an inert gas is supplied to the periphery of a reticle. In exposing the periphery of the reticle, the inert gas concentration in the space decreases. In addition, when the wafer stage moves at a high speed, the inert gas concentration decreases due to the influence of involvement, resulting in a variation in illuminance.